The invention relates to a laryngeal mask airway device used in unconscious patients to ventilate the lungs having an airway tube opening into the interior of a firm recessed ovoid bowl having attached at its periphery a cuff formation shaped to fit the actual and potential space surrounding the circumference of the inlet to the larynx. The cuff formation commonly takes the form of an inflatable cuff. The laryngeal mask is inserted into the unconscious patient's pharynx and is advanced until its tip is positioned within the upper esophagus and the cuff formation surrounds the circumference of the inlet to the larynx. The airway tube with the opening in the firm recessed bowl of the mask is then aligned with the laryngeal inlet to provide ventilation to the lungs.
FIG. 1 depicts a perspective view of a laryngeal mask 60 with a cuff formation in the form of an inflatable cuff 64. The laryngeal mask comprises two portions, an airway tube 62 and a mask portion 61 consisting of a bowl structure 68 that helps define a recessed interior space of the bowl structure 68 and a cuff formation that is an inflatable cuff 64 attached at a periphery of the bowl structure 68. The airway tube 62 has a proximal orifice 72 with suitable adapter for connection to respiratory equipment. The airway tube 62 is joined to the mask portion 61 and has fluid communication with an aperture 74 within the recessed ovoid bowl 68 of the laryngeal mask 60. The inflatable cuff 64 can be filled with fluid through an inflation line 76 with a pilot balloon/one-way valve 78 and the cuff formation (here depicted as an inflatable cuff 64) forms a seal with the pharynx surrounding the circumference of the inlet to the larynx.
FIG. 2A is a front view of a mask portion 61 with bowl structure 68 and cuff formation. FIG. 2A depicts descriptors for the different portions of a cuff formation, including proximal portion 80, lateral portion 82, and distal portion 84. Also identified are the midline most proximal point 85 of the cuff formation and the midline most distal point 86 of the cuff formation.
FIG. 2B is a front view of the same mask portion 61 as in FIG. 2A and depicts length measurements. FIG. 2B depicts the entire length 126 of the mask portion 61, the length 130 of the distal one-half of the mask portion 61, and the length 132 of the distal one-third of the mask portion 61.
FIG. 2C is a front view of the same mask portion 61 as in FIG. 2A and depicts a medial line 136 that passes through the midline most proximal point 85 of the mask portion 61 and through the midline most distal point 86 of the mask portion 61. FIG. 2C also depicts a midway-dividing line 138 corresponding to the length measurement 130 and dividing the mask portion into a proximal half 140 and a distal half 142. The distal one-third of the mask portion corresponding to the length measurement 132 is indicated by a demarcation line 139.
FIG. 3 depicts a side view of the anatomy of the human pharynx shown by dashed lines illustrating the anatomical relations of a laryngeal mask that is inserted in an unconscious patient. The distal portion 84 of the cuff formation is within the upper esophagus 18, contacting the mucosal surfaces of the esophageal walls 17, and the distal portion 84 lies directly behind the cricoid cartilage 15. The proximal portion 80 of the cuff formation rests against the base of the tongue 11. The epiglottis 12 may enter the recessed space of the bowl interior. The inflatable cuff 64 surrounds the laryngeal inlet 13 that leads to the vocal cords 14 and the trachea 16. The airway tube 62 emerges from the mouth 10 and may be connected to respiratory equipment.
FIG. 4 demonstrates a front view of human head and neck anatomy shown by dashed lines illustrating the anatomical relations of a laryngeal mask that is inserted in an unconscious patient. The inflatable cuff 64 and bowl structure 68 occupy the lower pharynx bounded laterally by pharyngeal walls 24 that funnel downwards forming esophageal walls 17 and the esophagus 18. The inflatable cuff 64 and bowl structure 68 lie posterior to the larynx with cricoid cartilage 15 and thyroid cartilage 23. The distal portion of the inflatable cuff 64 enters the esophagus 18 posterior to the cricoid cartilage 15. The airway tube 62 comes out of the mouth 10 and may be connected to respiratory equipment. Superficial landmarks include the sternocleidomastoid muscles 20, clavicle bones 21, and manubrium of the sternum 22.
The laryngeal mask occupies the lower pharynx of an unconscious patient with an inflatable cuff 64 adapted to fit the space surrounding the circumference of the inlet to the larynx. The airway tube 62 provides respiratory gases through its distal orifice within the recessed bowl structure 68 that is located opposite the laryngeal inlet leading to the lungs. The laryngeal mask airway device occupies the lower pharynx and upper esophagus but does not go through the vocal cords into the trachea; consequently, the laryngeal mask presents two potential problems.
First, if the vocal cords close for any reason, then the aperture or space or void between the two vocal cords (called the glottis or glottic space) may become extremely small or be abolished; and it may be difficult or impossible to provide ventilation for the patient despite correct positioning of the laryngeal mask. The vocal cords are located in the fluid channel for oxygen traveling through a laryngeal mask airway device to the lungs and the vocal cords form an aperture in such fluid channel for oxygen delivery to the lungs. It is possible for the area of the glottis to be sufficiently reduced or narrowed such that the ability of a laryngeal mask airway device to provide adequate oxygen and ventilation for an unconscious patient either by spontaneous ventilation or by positive pressure ventilation will be severely compromised.
Second, the laryngeal mask airway device is not as protective for the patient as is a cuffed endotracheal tube against pulmonary aspiration of gastric contents. Pulmonary aspiration of gastric contents describes the physical process of gastric contents, liquid or solid, entering the lungs, thereby obstructing the airway passages or damaging the delicate lung alveoli; and such pulmonary aspiration may be life-threatening or fatal for the patient. The cuffed endotracheal tube is an airway device that passes between the vocal cords into the trachea; and the portion of the endotracheal tube that enters the trachea may have an inflatable cuff that forms a seal with the interior walls of the trachea that may prevent gastric contents from contaminating the lower airways and lung alveoli. Since the laryngeal mask does not pass through the vocal cords, it does not provide such protection.
Previous inventions of laryngeal masks targeting the advantage of decreasing the risk of pulmonary aspiration of gastric contents have included a tube called an evacuation tube or drainage tube added to the laryngeal mask construction. Such evacuation tube or drainage tube has a distal orifice near the tip of the mask, travels through the tip of the mask parallel to the medial line, and arrives at the tip of the mask traveling in front of, within, or behind the back of the recessed ovoid interior space of the laryngeal mask bowl. The proximal orifice of the evacuation tube or drainage tube is adjacent to the proximal orifice of the airway tube. Following insertion of such mask, the distal orifice of the tube, positioned in the upper esophagus, can capture regurgitating gastrointestinal contents and, through the interior of the tube, evacuate gastrointestinal contents to the outside of the patient and away from the lungs. Such a tube that is part of the laryngeal mask construction can also facilitate insertion of orogastric tubes from outside the patient directly to the upper esophagus; and such orogastric tubes can be advanced into the esophagus and stomach in order to passively drain or to actively suction liquid gastrointestinal contents to outside the patient and to reduce the patient's risk for pulmonary aspiration of gastric contents.
Previous inventions of laryngeal masks targeting the advantage of decreasing the risk of pulmonary aspiration of gastric contents have enhanced the cuff formation to increase the seal pressure with the pharyngeal and esophageal mucosal surfaces, have added tubes and constructions extending beyond the tip of the cuff formation, and have included methods to occlude the esophageal lumen such as with esophageal blockers.
The first commercially available laryngeal mask with a drainage tube and specifically enhanced cuff formation was the PROSEAL laryngeal mask (from Teleflex Inc., North Carolina, USA) developed by Dr. Archibald J. Brain—see, e.g., U.S. Pat. Nos. 4,509,514; 5,241,956; and 6,439,232 B1; and Brain, et al., “The LMA ‘ProSeal’—a laryngeal mask with an oesophageal vent,” 84 Br. J. Anaesth. 650-654 (2000). The present inventor used this laryngeal mask in clinical practice of anesthesiology and performed research of the PROSEAL laryngeal mask. The present inventor investigated clinical characteristics of laryngeal mask design with the presence of a drainage tube passing through the central portion of the distal cuff formation and investigated clinical characteristics of laryngeal mask design with enhanced cuff formation.